1. Field of the Invention
This invention relates to planar magnetron sputtering devices.
2. Discussion of Prior Art
FIGS. 1 and 2 are cross-sectional and perspective views respectively of a representative prior art planar magnetron sputtering device comprising inner magnet 10 and outer magnet 12 (both of which usually comprise a number of sections) where the magnets are shunted by an iron pole plate 14. Disposed above the magnetic structure is a cathode or target 16 (not shown in FIG. 2). The magnetic lines of force are as shown in FIG. 1 where they exit from and return through cathode 16, a similar technique being employed in U.S. Pat. No. 3,878,085 where the magnetic lines also enter and exit from the cathode surface.
An electric field is established between (a) a ring-like anode 17, which may be disposed around and spaced from cathode 16, (or the chamber wall may serve this function) and (b) the cathode whereby electrons are removed from the cathode. Due to the configuration of the lines of magnetic force (the illustration of which is approximate), the removed electrons tend to concentrate in regions A where the lines of force are substantially parallel to the upper surface of target 16. There the electrons ionize gas particles which are then accelerated to the target to dislodge atoms of the target material. The dislodged target material then typically deposits as a coating film on an object to be coated. Assuming the object to be coated is in strip form or is mounted on a strip moving in the direction of the arrow shown in FIG. 2, the object will be uniformly coated, the strip being narrower in width than the length of the sputtering device.
Once the ionizing electrons are removed from the target, they travel long paths because they circulate in a closed loop defined between inner magnet 10 and outer magnet 12, the loop being above target 16. Hence, the electrons are effective in ionizing the gas particles. However, since most of the ionizing electrons are concentrated in regions A, the ionized gas particles will mainly erode cathode 16 in regions A'. Such uneven disintegration of the target is undesirable in that the target materials are most often extremely pure and accordingly, very expensive.
Another prior art arrangement is shown in cross-section in FIG. 3 where parallel magnets 18 and 20 are employed with pole pieces 22 and 24. However, this configuration is essentially the same as that of FIGS. 1 and 2 in its function and is subject to the same shortcomings.